Arc Fault Detection

Arc Fault Detection Devices


Recommended as a means of providing additional protection against fire

Regulation 421.1.7 of BS 7671 has been introduced recommending the installation of arc fault detection devices (AFDDs) to mitigate the risk of fire in AC final circuits of a fixed installation due to the effects of arc fault currents.

Accidental Domestic Fires UK total: Approximately 19,300 Accidental domestic fires of electrical origin

Accidental electrical Dwelling Fires Accidental electrical dwelling Fires: 14,186 (53.4% of all accidental dwelling fires) | Of which caused by faulty appliances and leads: 3667 (25.9% of electrical fires)

Our AFDD protects against:

What is an Arc Fault?

An arc-fault occurs when loose or corroded connections make intermittent contact and causes sparking or arcing between the connections. This translates into heat, which will break down the insulations of the wire and potentially trigger an electrical fire. Such arc’s can range in power and vary a great deal in strength and duration. 

Types of Arc Faults

Parallel arc faults are found with damage caused to insulation which allows current to flow between conductors, usually between phase and neutral.

Series arc faults are found in loose terminal connections, damaged cords or frayed/damaged conductors. These arc’s are created in one conductor only, either phase or neutral.

What is an Arc Fault Detection Device (AFDD)?

Arc Fault Detection Devices use digital electronics to analyse the waveform of an A.C. circuit to detect arc faults.

The device continuously monitors the circuit for different variations including the duration of an arc and the waveform. Once the device detects an irregular fault the device trips and disconnects the circuit, reducing the chance of it over heating and potentially causing an electrical fire.

Where Should AFDDs be Used?

AFDDs are recommended to be fitted in consumer units or distribution boards in premises with sleeping accommodation, locations where there is a risk of fire due to the activity within, premises constructed of combustible materials, fire propagating structures such as high rising buildings and locations where there are irreplaceable goods. See 421.1.7 for further details.

What Types of Circuits can AFDDs be Used on?

The regulations state AC single-phase circuits not exceeding 230V, that includes ring circuits, radials etc.

What is an AFR?

The M2 AFR is an arc fault detection device combined with short circuit, overload and earth leakage detection.

Installer Guidance

If used, an AFDD/AFR shall be placed at the origin of the circuit. Examples of use: premises with sleeping accommodation; where there is risk of fire; combustible construction materials; fire propagating structures; locations with endangering of irreplaceable goods.

Potential Causes of an Arc Fault Could be?

Trapped/Damaged Cables

Loose Terminations

Cable Wear

Damage Caused by Construction Work

Detection Characteristics

When all three inputs are simultaneously sustained for at least 100mS, the AFDD will trip. This maximises arc fault detection whilst minimising the risk of nuisance tripping.

A sustainable current of a certain magnitude

A minimum number of consecutive half cycles of arcing conditions

Presence of Hi-Lo asymmetrical frequency components

Technical Information

Tripping Characteristics

Tripping Characteristics M2